Automatic sprinkler systems are widely used for residential and commercial properties to control sprinkler heads when and for how long one or more watering stations should be turned on.
To conserve water, it is desirable to turn a sprinkler system off altogether when there is sufficient amount of rain. After rain has stopped and enough rain water evaporated, the sprinkler system should go back to its normal programmed mode so that plantation that is covered by sprinklers does not dry out and wither.
Manually turning off the sprinkler systems when there is rain and turning them back on a day or a few days after the rain will work in principle. However, remembering to turn off and on the sprinkler system can be a challenge. Forgetting to turn off a sprinkler system after rain will waste water, but forgetting to turn the sprinkler system back on a few days after the rain can potentially ruin a garden, thus deterring people from trying this water conservation activity.
There are primarily three types of rain shut off sprinkler systems on the market. One is weight based, another is conductivity based and the other is volume based.
For the weight based system, a container with an open top collects rain water and. Once the water inside the container reaches certain predetermined weight, the weigh of the container will push down far enough on an electrical switch that is mechanically attached to the container bottom to turn off the switch which in turn cuts off electricity to the sprinkler heads. The problem with this system is that the container will not just collect rain water, it will also catch falling objects such as leaves. A sprinkler system that is turned off not because of rain water but because of falling leaves can potentially ruin a backyard or flower beds. As such, the system is not very reliable.
For the conductivity based system, a container with an open top has two electrically conductive members are positioned apart inside the container. Conductivity between the electrically conductive members is constantly measured, and will change based on whether there air between two electrically conductive members or water. Changing in conductivity due to presence of water or air will turn off or on power to the sprinkler heads. The problem with this system is that the consistency of conductivity of water. When there is impurity in the water (e.g. dust, bird dropping, etc), conductivity changes which may alter the on/off function yielding an unreliable rain shut-off switch that can potentially ruin a garden.
For the volume based system, an electrical switch is situated in proximity of a block of material whose volume can expand once moisture is absorbed. Among many materials found in daily lives, cork is one such material that can easily expand when it absorbs water. The expandable material and the switch are placed inside an open top container. The cork will start expanding once the container receives rain water. After it expands to a predetermined size, the electrical switch is activated by the expanding material to turn off the sprinkler heads. The problem is that expandable materials typically have a life: after so many dry-wet cycles, their expandability with relation to the amount of water may change causing reliability issues.
To summarize, there is a need for a liquid or water activated electrical switch or a rain shut off system to automatically and reliably detect there is enough rain fall to turn off a sprinkler system and to automatically detect there is sufficient water evaporation to turn the sprinkler system back on.